A holographic recording medium on which data are recorded holographically has been invented (e.g. see JP-A-2004-029476). The holographic recording medium is a photosensitive recording medium in which holographic recording layers each made of a photosensitive material are provided on a disc-shaped support. Data are multiplexedly recorded on the holographic recording medium as interference fringes of laser light, so that the holographic recording medium can obtain a larger data recording capacity than that of a DVD which is a recording medium heretofore widespread. Exposure of the holographic recording layers to light or deposition of dust on the holographic recording layers exerts a bad influence on the performance of the holographic recording medium. For this reason, the holographic recording medium is dealt with in the condition that the holographic recording medium is stored in a cartridge having a light-shielding function and a dustproof function (e.g. see JP-A-2003-317422 (corresponding to US 2003/0198177 A1)). In addition, there has been known a cartridge having a cartridge housing, a shutter plate and a cover (e.g. see JP-A-2003-317424).
In the invention described in JP-A-2004-029476, the holographic recording medium is stored in a cartridge similar to the cartridge of a DVD-RAM. The cartridge is made of a material low in transmittance of light rays in a wavelength range exerting influence on the holographic recording layers. Although JP-A-2004-029476 did not give any description on the detailed configuration of the cartridge, it may be conceived that the cartridge has the same configuration as that of the cartridge described in JP-A-2003-317422 (corresponding to US 2003/0198177 A1).
In the invention described in JP-A-2003-317422 (corresponding to US 2003/0198177 A1), the cartridge is made of a material capable of blocking light with a color sensitive to the holographic recording layers, and a sponge-like light-shield material is stuck to a mating portion of a movable portion for exposing the holographic recording medium to the outside. In addition, in the description, the cartridge is provided with a cartridge body for receiving a recording medium therein in a desirably rotatable state, an opening provided in the cartridge body and for exposing part of the recording medium to the outside, and a shutter for opening/closing the opening.
In the invention described in JP-A-2003-317424, overlap is provided between the circumference of the opening of the cartridge housing and the shutter plate and between the shutter and the circumference of the opening of the cover. This double-overlap prevents dust from entering from the outside.